Why do we want reflow profiles?
Whereas most makers are a minimum of considerably aware of the idea of utilizing a soldering iron to soften solder onto through-hole parts, the world of floor mount is sort of totally different. The method usually entails spreading a skinny layer of solder paste onto the PCB’s uncovered pads, putting the parts, after which reflowing, or melting, the solder paste to make the connections. This final step requires a number of temperature phases to be reached over the course of some minutes which ensures stable bonding and prevents part injury.
From “Reflow Soldering” on Wikipedia
Some current initiatives make the most of repurposed toaster ovens with modified timing circuitry, however Crimson Dynamo wished one thing that might be simply expanded to accommodate all kinds of PCB sizes. His thought was to construct a reflow hotplate that heats boards through direct contact quite than scorching air- all whereas having clever profiles which might be utilized over time.
Constructing a heating circuit
To generate sufficient warmth, Crimson went with a pair of 400W, 240V heater plates together with a 10A relay, thermistor (temperature sensor), and metal plate for every. When present is utilized to the plates via the closed relays, they can rapidly ramp up their temperature which might then be tempered via a microcontroller and thermistor. A cut-out protector was additionally positioned inline to take away energy from the plates within the occasion of thermal runaway.
The controller board
Based mostly on an ESP32 Dev Package V4, the person interface board is answerable for presenting choices to the person through a 0.96″ OLED display screen and dealing with the choice. As soon as an choice has been chosen with a rotary encoder, the microcontroller closes the relays after which switches them on or off relying on the present thermistor studying and the goal temperature from the profile due to a PID loop.
Hotplates and enclosures
The excessive voltages and temperatures concerned on this mission led Crimson so as to add a number of essential security options to his enclosure. First, the hotplates are raised with a sequence of standoffs from the bottom, thus stopping them from heating their environment an excessive amount of. Second, all the high-voltage internals are recessed right into a 3D printed plastic enclosure to assist scale back shock dangers. And eventually, the metallic construction inside is absolutely grounded as yet one more security measure.
Creating profiles
Crimson started by calibrating his thermocouples with a check mode he programmed which slowly ramps up the voltage being utilized to the hotplates. It then permits the person to measure the true hotplate temperature with a thermometer and file the 2 values. This continues till diploma values starting from 25C all the best way to 200C have been created and related to one another in code. After calibration has completed, thermal profiles, or arrays of temperatures over time, may be loaded into this system and chosen from the display screen.
To learn extra about this good hotplate reflow station, take a look at Crimson Dynamo’s mission write-up right here.
